Nanoscale Origin of the Soft-to-Hard Short-Circuit Transition in Inorganic Solid-State Electrolytes

Understanding and overcoming the chemomechanical failures of polycrystalline inorganic solid-state electrolytes (SSEs) are critical for next-generation all-solid-state batteries. Yet, so far, the nanoscale origin of SSEs' chemomechanical failure under operation conditions remains a mystery. Here, by using in situ electron microscopy, we decipher the nanoscale origin of the soft-to-hard short-circuit transition─a conventionally underestimated failure mechanism─caused by electronic leakage-induced Li⁰ precipitation in SSEs. For the first time, we directly visualize stochastic Li⁰ interconnection-induced soft short circuits, during which the SSEs undergo the transition from a nominal electronic insulator to a state exhibiting memristor-like nonlinear conduction (electronic leakages), ultimately evolving into hard short circuits. Furthermore, we first capture intragranular cracking caused by Li⁰ penetration, demonstrating that fully wetted Li⁰ can fracture polycrystalline oxide SSEs via a liquid-metal embrittlement-like mechanism. Guided by these insights, we show that incorporating an electronically insulating and mechanically resilient 3D polymer network into an inorganic/polymer composite SSE effectively suppresses Li⁰ precipitation, interconnection, and short circuits, significantly enhancing its electrochemical stability. Our work, by elucidating the soft-to-hard short-circuit transition kinetics of SSEs, offers new insights into their nanoscale failure mechanisms.